문제 link
https://www.hackerrank.com/challenges/sql-projects/problem
Code link
https://github.com/JamesJung01/Hackerrank_sql/blob/main/02_Medium/SQL_Proejct_Planning.sql
SET sql_mode = ''; SELECT Start_Date, End_Date FROM (SELECT Start_Date FROM Projects WHERE Start_Date NOT IN (SELECT End_Date FROM Projects)) a, (SELECT End_Date FROM Projects WHERE End_Date NOT IN (SELECT Start_Date FROM Projects)) b WHERE Start_Date < End_Date GROUP BY Start_Date ORDER BY DATEDIFF(End_Date, Start_Date), Start_Date